Recently, there has been a tendency to manufacture semiconductor devices such as flash memories in a highly integrated manner. Thus, pattern sizes of semiconductor devices are becoming finer and finer. To form such a fine pattern, a predetermined treatment process, such as an oxidation process or a nitridation process, may be performed on a substrate as a process included in a semiconductor device manufacturing process.
As a method of forming such a pattern, there is a process of forming a groove between circuits and forming a liner film or wires in the groove. Such grooves are being formed to have higher aspect ratios as pattern sizes become finer and finer.
To form the liner film and the like, it is required to form a film having high step coverage such that the film has a uniform film thickness on an upper side surface, a middle side surface, a lower side surface and a bottom portion of the groove. By forming the film having high step coverage, a semiconductor device may have uniform characteristics, thereby suppressing a deviation in the characteristics of the semiconductor device.
There have been attempts to form a film in a groove having a high aspect ratio by heating a gas or converting the gas into a plasma state, but a film having high step coverage is difficult to form. As a method of forming a film having high step coverage, a method of alternately supplying at least two types of processing gases and reacting the supplied gases on a surface of a substrate to form a film has been introduced.
Since the characteristics of a semiconductor device need to be made uniform, a gas should be uniformly supplied within a plane of the substrate when a thin film is formed. To this end, for example, a single-wafer-type apparatus is used as a substrate processing apparatus capable of uniformly supplying a gas to the surface of the substrate to be processed. In the single-wafer-type apparatus, for example, a shower head configured to supply a gas to a substrate is installed to supply a gas to the substrate more uniformly and a buffer space is formed in the shower head.
When the above method is performed by a single-wafer-type apparatus including a shower head, residual processing gases should be purged (discharged) using an inert gas when each of the processing gases is not supplied so as to prevent the processing gases from reacting with each other on locations except for a surface of a substrate. However, such a purge process decreases a film forming speed. Thus, it may be effective to discharge residual gases by supplying a large amount of a purge gas in order to reduce a film forming time.
Also, according to an embodiment of the present invention, buffer spaces corresponding to various types of gases may be formed in a shower head to prevent processing gases from being mixed with each other. However, in this case, since the system has a complicated structure, maintenance is not easy and costs increase. Accordingly, it is practical to use a shower head including a common buffer space for a plurality of gases.
As described above, a common shower head may be used for a plurality of gases to uniformly supply gases and form a film at a high speed, and a purge gas may be supplied at a high flow rate to discharge residual gases. However, when the shower head is cooled by the purge gas, by-products are likely to be attached to the inside of the shower head. The attached by-products may change into particles which have a bad influence on the features of a film formed on a substrate.